Review ofRemovable
Partial Dentures
Review of
RemovablePartial Dentures
Lovely MMDS(Prosth) Dip NB (Prosth)
Associate Professor and HOD In-chargeSree Mookambika Institute of Dental Sciences
Kulasekharam, Tamil Nadu
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Review of Removable Partial Dentures
2005, Lovely MAll rights reserved. No part of this publication should be reproduced, stored in aretrieval system, or transmitted in any form or by any means: electronic, mechanical,photocopying, recording, or otherwise, without the prior written permission of theeditor and the publisher.
This book has been published in good faith that the material provided by editoris original. Every effort is made to ensure accuracy of material, but the pub-lisher, printer and editor will not be held responsible for any inadvertent error(s).In case of any dispute, all legal matters are to be settled under Delhi jurisdictiononly.
First Edition: 2005
ISBN 81-8061-577-4Typeset at JPBMP typesetting unitPrinted at Gopsons Papers Ltd., A-14, Sector 60, Noida
Dedicated toMy Almighty GOD
andMy Family
FOREWORD
The ever-increasing number of textbooks and other literature,which is available for reference to the Dental profession, eachyear makes it difficult for the average undergraduate dentalstudent to prepare adequately for their examinations.
Often, the diverging views of the authors, on a particularsubject, leave the candidates in confusion regarding the correctanswer to be given. This is more evident when answering essayand short note type questions.
Dr. Lovely has taken great pains to tackle this problem byarriving at acceptable answers to the above-mentioned typesof questions. The systematic and topic-wise layout of theanswers makes it easy for the students to reproduce.
Even though many guidebooks are available in the marketto help the students to answer the MCQ type questions, this isto my knowledge the first such book to guide the students inanswering questions in the essay and short note format.
I am happy to introduce Review of Removable PartialDentures to the present undergraduate students as well as theDental Profession in general. I hope it will lend a helping handto many aspirants of higher education in Dentistry.
Prof. George Paulose MDS (Prosthodontics)Principal, PMS Dental College,
Golden Hills, Vengode, Vattapara,Trivandrum
PREFACE
Review of Removable Partial Dentures is the second book inthe examination review series in Prosthodontics being broughtout as study aids for the undergraduate dental studentappearing for the BDS university examinations.
It is meant as a continuation of the first book Review ofComplete Dentures which was published earlier and is alsosimilarly intended as a revision tool for students before theuniversity examinations. However, I hope that this book willalso be useful for practising dentists and postgraduate studentsto keep up with the latest in the subject.
This book helps the student to get an idea of how thequestions are framed and how to answer in a structured manner.The questions in this book are from actual universityexamination question papers sourced from all over the country.The answers are formulated after much painstaking referencewith all the standard textbooks in Removable Partial Dentures.
The inspiration for this book was the need that I myselffelt, as a student, for such a revision tool, just prior to myexamination, and therefore, I hope that the present studentswill take full benefit of it.
I thank God for enabling me to bring out this book in time.I especially thank Prof. K. Chandrasekharan Nair for hisinvaluable help and time in going through and correcting theproofs of this review. Thanks are due to Dr. Krishna MohanReddy, Dr. Binoy, Dr. Murukan, Dr Jitendra Jethwani,Dr. Gayathri and all of my friends and colleagues all over Indiawho sent me question papers from their Universities. Specialthanks to my department colleague, Dr. James. R. Rex, for hishelp in drawing the diagrams, which are included in this review.I also thank my department colleagues Dr. Mohan Kumar,
Dr. K.C. Nayar, Dr. Prashanth, Dr. Seema and Dr. Akhila fortheir encouragement and help. Last but not least, I thank myhusband, parents and in-laws for their encouragement andsupport.
Lovely M
x Review of Removable Partial Dentures
CONTENTS
ESSAYS ........................................................................... 1-158Explain the importance of diagnostic and treatmentplanning phases in RPD ................................................................ 3
List various classifications of RPD and the basis forclassifying partially edentulous situation. Enumeratemerits of Kennedys classification ............................................... 10
Discuss various classifications of partially edentulous ridge.Explain Kennedy Applegates modification ............................... 12
Define major connector. Explain in detail its requirements.Describe maxillary major connectors in detail .......................... 17
Describe mandibular major connectors. Add a note on theadvantages and disadvantages of each mandibular majorconnector ....................................................................................... 24
Explain in detail various types of minor connectors.Add a note on the functions of minor connector ......................... 30
Define a direct retainer. List the functions of a circumferentialclasp and various parts as related to function. Describe thevarious types of retainers ............................................................ 37
Enumerate various factors affecting retention in directretainers. Add a note on gingivally approaching claspsand RPI system ............................................................................. 46
Define rest and rest seat. Give its location. Describevarious types of rests and their function ..................................... 51
Explain the various impression techniques used in thefabrication of RPD. Describe the functional impressiontechnique using Korecta wax ....................................................... 59
What is the importance of distal extension impressionprocedure in partial denture? List factors influencingsupport of distal extension base. Explain in detail fluidwax impression technique ........................................................... 65
Explain importance of mouth preparation in cast partialdenture designing and add a note on various proceduresand its significance in designing. ................................................ 70
Enumerate factors affecting design of RPD and add anote on design aspects in Kennedys Class I situations ............. 77
Mention and justify the components indicated forKennedys Class I and II RPD. How does it differfrom Class III design .................................................................... 82
Discuss the problems that are encountered in makingRPD for a Kennedys Class I mandibular situation.Describe the steps in the design of a Kennedys Class Imandibular situation .................................................................... 88
Define surveyor and surveying. List aims and objectives ofsurveying. Add a note on factors affecting path of insertion ..... 94
Explain the step by step procedure of surveying mastercast in RPD ................................................................................... 99
Draw a diagram of Ney surveyor. Label its parts. Listfunction of tools in surveyor. Describe how retentiveundercuts are located using a model surveyor and howthey affect the path of insertion ................................................. 105
Explain the three basic theories by which forces actingon RPD are distributed between soft tissue and teeth .............. 110
List various parts of RPD. Explain with diagram and listfunctions of each component in detail ....................................... 115
What are various forces acting on RPD? Enumeratedifferent methods in which stresses are controlled in RPD ..... 120
Explain steps in laboratory procedure for frameworkconstruction of cast partial denture .......................................... 126
Enumerate steps in clinical procedure for fitting theframe work of a cast partial denture ......................................... 134
What are the factors influencing magnitude of stressestransmitted to the abutment teeth .............................................. 137
Discuss the harmful effects of a wrongly designed RPDon a patient of 40 years .............................................................. 143
Despite shortcomings, alginate impression material enjoyspopularity among dentists. Discuss. Add a note on itsshortcomings and advantages ................................................... 147
Define immediate denture. Classify immediate dentures. Adda note on their advantages and disadvantages. Enumeratethe clinical steps in relation to immediate dentures ................ 153
SHORT NOTES........................................................... 159-334Diagnostic casts ......................................................................... 161
Indications and requirements of removable partial dentures . 162
xii Review of Removable Partial Dentures
Applegates rules ........................................................................ 164
Principles of RPD designing ...................................................... 165
Advantages and disadvantages of Kennedys classification ... 169
Abutment selection ..................................................................... 171
Periodontal aspects in mouth preparation ............................... 174
Dual impression ......................................................................... 179
Closed mouth impression .......................................................... 182
Impression trays ......................................................................... 183
Fluid wax functional impression .............................................. 184
Altered cast technique ................................................................ 186
Palatal major connector ............................................................ 190
Lingual bar ................................................................................. 192
Swing lock partial dentures ....................................................... 195
Linguoplate ................................................................................. 198
Occlusal rest/primary rest ......................................................... 200
Intracoronal retainer .................................................................. 203
Combination clasp ..................................................................... 205
Bar or roach clasp ...................................................................... 207
Embrasure clasp or modified crib clasp ................................... 210
Requirements of a clasp ............................................................. 212
Differences between wrought wire retentive clasp armsand cast circumferential clasp arms ......................................... 214
RPI system .................................................................................. 217
Stressbreakers/stress equalizers ............................................... 219
Acrylic dentures .......................................................................... 221
Tools in surveying ...................................................................... 223
Tripoding the cast ....................................................................... 224
Guide planes ............................................................................... 226
Survey lines ................................................................................ 228
Work authorization .................................................................... 232
Block out and relief ..................................................................... 235
Finish lines/butt joints ............................................................... 237
Infection control in clinical prosthodontics/safety indental laboratory ........................................................................ 240
Jaw relations in partial denture ................................................ 243
Contents xiii
Try-in of partial denture ............................................................. 246
Methods for establishing occlusal relationships inpartial denture ............................................................................ 248
Speech aids ................................................................................. 252
Direct indirect retention ............................................................. 254
Functions and requirements of minor connector ..................... 254
Tissue stops ................................................................................ 256
Bracing and reciprocation ......................................................... 257
Eliminating processing errors ................................................... 259
Polishing and finishing acrylic resin andcast partials ................................................................................ 262
Causes of failures in RPD .......................................................... 264
Comparison of occlusal and gingivally approachingclasp ............................................................................................ 265
Precision attachments/semirigid connectors ........................... 267
Saddles ........................................................................................ 271
Soldering ..................................................................................... 275
Support ........................................................................................ 278
Importance of X-ray in RPD ...................................................... 280
Compare and contrast acrylic with cast partialdenture alloys ............................................................................. 283
Impression materials used in RPD ........................................... 286
Differences between tooth supported and tooth-tissuesupported denture ....................................................................... 291
Blatterfeins designing of major connector ............................... 292
Differences between Ney and Jelenco surveyors ..................... 294
Kennedy class iv arches ............................................................. 296
Possible movements of partial denture .................................... 298
Relining ....................................................................................... 301
Rebasing ..................................................................................... 304
Tooth replacements .................................................................... 305
Fixed removable partial dentures ............................................. 310
Casting ........................................................................................ 312
Post insertion observation ......................................................... 315
Splints ......................................................................................... 320
Radiation carrier ........................................................................ 323
xiv Review of Removable Partial Dentures
Guiding flange ............................................................................ 324
Types of removable partial denture .......................................... 325
Obturators ................................................................................... 330
Armed clasps .............................................................................. 333
Index ...................................................................................... 335
Contents xv
Essays
2 Review of Removable Partial Dentures
Essays 3
EXPLAIN THE IMPORTANCE OF DIAGNOSTIC AND TREATMENTPLANNING PHASES IN RPD
Diagnosis and Treatment Planning
Diagnosis is the examination of the physical state, evaluationof the mental or psychological makeup and understanding theneeds of each patient to ensure a predictable result.
Treatment planning means developing a course of action thatencompasses the ramifications and sequelae of treatment to servethe patients needs.
Oral Examination Includes Evaluating
1. Carious lesions and defective restorations.2. Testing for pulp vitality.3. Test for sensitivity to percussion.4. Mobility.5. Pocket depth, inflammation and amount of attached
gingiva of the abutment teeth.6. Any tori, exostoses, sharp or prominent bony areas, soft or
hard tissue undercuts and enlarged tuberosities.
Other Diagnostic Aids Required
Radiographs of the abutment teeth and the residual ridgeareas.
Mounted casts: To evaluate for the presence of extrudedteeth, malposed teeth, reduced interarch space andunfavourable occlusal plane.
Evaluation of Caries and Existing Restorations
1. All caries lesions need to be restored with intracoronalrestoration.
2. Extruded tooth above the occlusal plane need to be restoredwith an extra coronal restoration to improve the occlusalplane.
3. If rest seat need to be prepared a cast metallic restoration ispreferred as restoration.
4 Review of Removable Partial Dentures
Evaluation of Pulp
An electric pulp tester and thermal tests are used to detectpulpal necrosis or pulpitis.
Endodontically treated tooth, if used as an abutment,should be evaluated for the success of endodontictreatment.
Evaluation of Sensitivity to Percussion
Sensitivity can be due to
1. Tooth movement caused by a prosthesis or the occlusion.2. A tooth or restoration in traumatic occlusion.3. Periapical or pulpal abscess.4. Acute pulpitis.5. Gingivitis or periodontitis.6. Cracked tooth syndrome.
Evaluation of Mobile Teeth
A mobile tooth used as an abutment tooth will have a poorprognosis unless mobility is eliminated.
Causes of mobility
1. Trauma from occlusion (reversible).2. Inflammatory changes in the periodontal ligament
(reversible).3. Loss of alveolar bone support (not reversible).
Abutment teeth can be splinted to decrease mobility only if
The combined splinted teeth with crowns provide anabutment with greater total periodontal support.
Splinting can be done if two or three retainable teeth arewidely placed.
Evaluation of Periodontium
Findings requiring periodontal treatment are
1. Pocket depth in excess of 1 mm with furcationinvolvement.
Essays 5
2. Gingivitis.3. Marginal exudate.4. Less than 2 mm of attached gingiva.5. High frenal attachment.
Periodontal treatments include
Root scaling, root planning with good home oral hygieneprocedures.
Gingivectomy, periodontal flap procedures and freegingival grafts.
Evaluation of Oral Mucosa
Ulceration, swelling, or colour change as red or white lesions.
Common tissue reactions in prosthesis wearing patients
1. Palatal papillary hyperplasia.2. Inflammatory papillary hyperplasia.3. Epulis fissuratum.4. Denture stomatitis.5. Trauma from occlusion.6. Soft tissue displacement.
Evaluation of Soft Tissue Abnormalities
1. High frenal attachment of labial frenum2. Hypertrophic lingual frenum3. Vestibular extension or ridge augmentation procedures
can be done.4. Xerostomia.
Evaluation of Hard Tissue Abnormalities
Torus Palatinus: A major connector can be selected and designedto circumvent the torus.
Torus Mandibularis: Occurring bilaterally on the lingual surfaceof the mandible, which needs to be surgically removed beforeconstruction of a removable partial denture.
6 Review of Removable Partial Dentures
Exostoses and Undercuts: Surgical correction by simplealveolectomy.
The maxillary tuberosities: Need to be surgically corrected ifsupport and stability of the prosthesis is affected.
Mandibular tuberosity: The mandibular lingual tuberosity is abony protuberance at the distal end of the mylohyoid ridge inthe third molar area. This should be surgically reduced.
Evaluation of Space for Mandibular Major Connector
A minimum of 7 to 8 mm of space should be available for alingual bar major connector and if less than 7 mm of space isavailable a lingual plate major connector should be used.
A periodontal probe with millimetre markings is used tomeasure the space in the lingual aspect. The millimetre depthis read at the point where the probe contacts the gingival margin.
Evaluation of Radiographic Survey
Abutment tooth is evaluated. Residual ridge is evaluated. Other factors as radiolucencies, radio opacities, root tips,
impacted tooth, endodontically treated tooth are evaluated.
Radiographic Evaluation of Abutment Teeth
1. Root length, size and form.
2. Crown/Root ratio: at least 1:1 is required for an abutmenttooth.
3. Lamina Dura: Should be checked for absence,discontinuity, partial loss or thickening of lamina dura.
4. Periodontal Ligament Space: A widening of the periodontalligament space with a thickening of the lamina duraindicates occlusal trauma and heavy function.Clinical mobility of the tooth may also be present with theabove findings.
Essays 7
5. Bone Index Areas: Bone index areas have a positive bonefactor which includes a supportive trabecular pattern, heavycortical layer, dense lamina dura, normal bone height and anormal periodontal ligament space.
Evaluation of Mounted Diagnostic Casts
1. Insufficient interarch distance,2. Irregular occlusal plane,3. Extruded or malposed teeth and4. Unfavourable maxillomandibular relationships are all better
visualised on mounted diagnostic cast.
1. Interarch Distance
A decrease in interarch distance occurs when tooth unopposedby occlusion tend to over erupt over a period of time carryingthe alveolar process with it. Surgical correction can be done.
2. Occlusal Plane
Occlusal plane irregularity if mild can be corrected byenameloplasty.
In extrusion greater than 2 mm the placement of an extra-coronal cast metallic restoration is indicated.
3. Traumatic Vertical Overlap
Akerly classification:
Type I The mandibular incisors extrude and impinge intothe palate.
Type IIThe mandibular incisors impinge into the gingivalsulci of the mandibular incisors.
Type IIIBoth maxillary and mandibular incisors inclinelingually with impingement of the gingival tissues of each arch.
Type IVThe mandibular incisors move or extrude into theabraded lingual surfaces of the maxillary anterior teeth.
8 Review of Removable Partial Dentures
Clinical symptoms: Abrasion, mobility, migration of the teeth,inflammation and ulceration of the gingiva and palatal mucosa.
Can be corrected by: Orthodontic and orthognathic combinedsurgical procedures.
Lingual plates that extend on to the lingual surfaces of themaxillary anterior teeth.
4. Malrelation of jaws
Maxillary and mandibular osteotomy procedures are useful tocorrect these problems.
5. Tipped or malposed teeth
Limited orthodontic procedures for minor tooth movement canbe used to upright the tipped tooth to allow the placement of anartificial tooth.
6. Occlusion
A discrepancy between centric jaw relation and maximum occlusalcontact, or centric occlusion should be evaluated and correctedby selective grinding or coronal reshaping of teeth to, producesimultaneous occlusal contacts.
Prosthesis need to be constructed at centric jaw relation when:1. Absence of posterior tooth contacts.2. Situation in which all posterior tooth contacts are to be
restored with cast restorations.3. Only a few remaining posterior contacts.4. Minimum alveolar support for all the remaining teeth
corrected by minimum occlusal equilibration.5. Anterior slide from centric jaw relation and symptoms of
traumatic occlusion of the anterior teeth.
Treatment planning
The treatment of the partially edentulous patient can be dividedinto five phases.
Essays 9
Phase I
1. Collection and evaluation of the diagnostic data.2. Treatment to control pain or infection.3. Biopsy or referral of patient.4. Development of a treatment plan.5. Education and motivation of patient.
Phase II
1. Removal of deep caries and placement of temporaryrestorations.
2. Extirpation of inflamed or necrotic pulp tissues.3. Removal of non-retainable teeth.4. Periodontal treatment.5. Construction of interim prosthesis for function or
aesthetics.6. Occlusal equilibration.7. Reinforcement of education and motivation of patient.
Phase III
1. Preprosthetic surgical procedures.2. Definitive endodontic procedures.3. Definitive restoration of teeth, such as cast metallic
restorations.4. Fixed partial denture construction.5. Reinforcement of education and motivation of patient.
Phase IV
1. Construction of removable partial denture.2. Reinforcement of education and motivation of patient.
Phase V
1. Post insertion care.2. Periodic recall.3. Reinforcement of education and motivation of patient.
10 Review of Removable Partial Dentures
Length of appointment: The length of this appointment canvary greatly, depending on the complexity of the problemspresented by the patient.
LIST VARIOUS CLASSIFICATIONS OF RPD AND THE BASIS FORCLASSIFYING PARTIALLY EDENTULOUS SITUATION.ENUMERATE MERITS OF KENNEDYS CLASSIFICATION
Various Classifications
Cummer 1921, Kennedy 1923, Bailyn 1928, Neurohr 1939, Mauk1942, Wild 1949, Godfrey 1951, Friedman 1953, Beckett 1953,Craddock 1954, Swenson and Terkla 1955, Skinner 1957, Austin1957, Walt et al 1958, Applegate-Kennedy 1960, Terkla and Laney1963, William Avent 1966, Fiset 1973, Costa 1974 and Osborneand Lammie 1974
Requirements of an acceptable method of classification
1. It should permit immediate visualization of the type ofpartially edentulous arch being considered.
2. It should permit immediate differentiation between thetooth-borne and tooth- tissue supported removable partialdenture.
3. It should be universally acceptable.
Support classification
Tooth-borne. Mucosa-borne. Tooth and mucosa-borne.
Kennedys classification
A world wide accepted classification is that devised by EdwardKennedy in 1923.
When used in conjunction with a support classification, ithelps to give a clear classification understanding about the type
Essays 11
of denture under consideration during a discussion on partialdentures.
The Kennedy classification is based on the relationship ofthe saddles to the natural teeth.
Kennedys classification has four main groups with modificationsexcept for Class IV
Class I: Bilateral free-end edentulous spaces posterior tothe natural teeth.
Class II: Unilateral free-end edentulous space posterior tothe natural teeth.
Class III: A bounded unilateral edentulous space havingnatural teeth at each end.
Class IV: A bounded edentulous space anterior to the naturalteeth.
Modifications
All classes, except Class IV, have modifications.Each modification is an additional edentulous area.
Examples of modifications: An additional edentulous area in Class I would be designated
as Class I modification 1. If two additional edentulous areas are present it could be
designated as Class I modification 2. A unilateral saddle with one additional edentulous area is
Class II modification 1. A unilateral bounded edentulous area with three additional
edentulous areas is Class III, modification 3.Class IV has no modifications.
Criteria for the Kennedys classification
1. The most posterior edentulous area determines the class.2. The size of the modification is not important.3. If a third molar is missing, and not to be replaced, it is not
considered in determining the class.
12 Review of Removable Partial Dentures
Merits of Kennedys classification
1. Allows visualization of partially edentulous arch.2. Differentiates between tooth supported and tooth tissue
supported.3. Type of design can be decided.4. Is universally accepted.5. Aids in discussing, identifying and planning the design.6. Easy to apply the system to any situation.7. Widely used system.8. Forms the basis for two other systems as Applegate Kennedy
and Swensons system.
Diagrams
Figure 1: Kennedys class I Figure 2: Kennedys class II
Figure 3: Kennedys class III Figure 4: Kennedys class IV
DISCUSS VARIOUS CLASSIFICATIONS OF PARTIALLYEDENTULOUS RIDGE. EXPLAIN KENNEDY APPLEGATESMODIFICATION
Several methods of classification of partially edentulous archeshave been proposed and are in use today. There are over 65,000
Essays 13
possible combinations of teeth and edentulous spaces inopposing arches.
No single method of classification can describe all thecombinations except the most basic types.
Kennedys method of classification is the most widelyaccepted classification of partially edentulous arches today.
A few other classifications
Cummers classification (1921)
First classification to be recognised by the dental profession.He classified partial dentures than edentulous spaces.
Four types:
1. Diagonal: 2 retainers diagonally opposite one another.2. Diametric: 2 retainers diametrically opposite one
another.3. Unilateral: 2 or more direct retainers on same side.4. Multilateral: 3 direct retainers on either side.
Charles. W. Bailyn (1928)
He emphasized the importance of support for partial dentures.AAnterior restorations where there were saddle areas
anterior to the bicuspids.PPosterior restorations where there were saddle areas
posterior to the canines.
Classification
Class I: Bounded saddle (Tooth supported).Class II: Free end saddle (Mucosa supported).Class III: Bounded saddle (More than three tooth missing).Example: If all posterior teeth from canines till molars aremissing with lateral incisors then the classification is AI P III.
14 Review of Removable Partial Dentures
Neurohrs Classification
Class I:
Variation I:a. Posterior missing, Anterior all teeth present.b. Posterior missing, some anterior teeth missing.Variation II:a. Anterior missing, All posteriors present.b. Anterior missing, some posteriors missing.
Class II: Division I has variation 1 and 2.Division II has variation 1 and 2.This classification is tooth tissue bearing.
Class III is edentulous state.
Friedmans system
AAnterior space.BBounded posterior space.CCantilever situation or a posterior free end saddle.
Osborne and Lammie
Class I: Mucosa borne.Class II: Tooth borne.Class III: Combination of mucosa borne and tissue borne.
Requirements of an acceptable method of classification
1. It should permit immediate visualization of the type ofpartially edentulous arch being considered.
2. It should permit immediate differentiation between the tooth-borne and the tooth-and tissue-supported removable partialdenture.
3. It should be universally acceptable.
Kennedys classification
The Kennedy method of classification was originally proposedby Dr. Edward Kennedy in 1923 and attempts to classify the
Essays 15
partially edentulous arch suggesting principles of design for agiven situation.
Kennedy divided partially edentulous arches into four maintypes.
Class I
Bilateral edentulous areas located posterior to the remainingnatural teeth.
Class II
A unilateral edentulous area located posterior to the remainingnatural teeth.
Class III
A unilateral edentulous area with natural teeth remaining bothanterior and posterior to it.
Class IV
A single, but bilateral (crossing the midline), edentulous arealocated anterior to the remaining natural teeth.
Modifications
All classes, except Class IV, have modifications.Each modification is an additional edentulous area.
Examples of Modifications
An additional edentulous area in Class I would be designatedas Class I modification 1.
If two additional edentulous areas are present it could bedesignated as Class I modification 2.
Class II modification 1: a unilateral edentulous area withone additional saddle.
Class III, modification 3 would be a unilateral boundededentulous area with three additional edentulous areas.
Class IV has no modifications.
16 Review of Removable Partial Dentures
Criteria for the Kennedys classification
1. The most posterior edentulous area determines the class.2. The size of the modification is not important.3. If a third molar is missing, and not to be replaced, it is not
considered in determining the class.
Merits of Kennedys classification
a. Allows visualization of partially edentulous arch.b. Differentiates between tooth supported and tooth tissue
supported.c . Type of design can be decided.d. Is universally accepted.e. Aids in discussing, identifying and planning the design.f. Easy to apply the system to any situation.g. Widely used system.h. Forms the basis for two other systems as Applegate Kennedy
and Swensons system.
Applegates rules for applying the Kennedy classification
Applegate provided the following eight rules for the easyapplication of the Kennedy method:
Rule 1. Classification should follow rather than precede anyextractions of teeth that might alter the originalclassification.
Rule 2. If a third molar is missing and not to be replaced, it isnot considered in the classification.
Rule 3. If a third molar is present and is to be used as anabutment, it is considered in the classification.
Rule 4. If a second molar is missing and is not to be replaced, itis not considered in the classification.
Rule 5. The classification is always determined by the mostposterior edentulous area or areas.
Essays 17
Rule 6. Edentulous areas other than those determining theclassification are referred to as modifications andare designated by their number.
Rule 7. The extent of the modification is not considered, onlythe number of additional edentulous areas.
Rule 8. There can be no modification areas in Class IV arches.(Another edentulous area lying posterior to the singlebilateral area crossing the midline would determinethe classification.)
Applegate added two more classes to Kennedys existingclassification
Class V
This is an edentulous area, bounded anteriorly and posteriorlyby natural teeth, in which the anterior abutment is not suitablefor support.
Class VI
This is an edentulous situation in which the abutment tooth iscapable of total support. (As in young patients.)
DEFINE MAJOR CONNECTOR. EXPLAIN IN DETAIL ITSREQUIREMENTS. DESCRIBE MAXILLARY MAJOR CONNECTORSIN DETAIL
Definition
A major connector is the unit of the partial denture that connectsthe parts of the prosthesis located on one side of the arch withthose on the opposite side. It is that unit of the partial dentureto which all other parts are directly or indirectly attached.
Requirements of major connector
1. Major connectors must be rigid to transfer forcesuniformly over the entire supporting structures.
18 Review of Removable Partial Dentures
2. Prevents movement of the denture base by its rigidity.3. Aids the other components of the partial denture to
function effectively.4. They should not be placed on excessively movable tissues.5. Should be placed 4 mm away from gingival margin in
mandibular and 6 mm away from gingival margin inmaxillary.
6. Should not be placed on bony and soft tissue prominences.7. Relief should be provided beneath a major connector if
necessary.8. The borders of the palatal connector should be 6 mm away
from gingival margins and should be parallel to their meancurve.
9. The anterior and posterior borders should cross midline atright angles.
10. Minor connectors must cross gingival tissues, at nearly aright angle while joining the major connector.
11. An anterior palatal strap or the anterior border of a palatalplate should be located as far posteriorly to avoidinterference with the tongue.
12. The anterior border of such palatal major connectorsshould follow the valleys between the rugae.
13. Should maintain oral health.14. All borders should taper towards soft tissue.15. Should be made from an alloy compatible with oral tissues16. Thickness of metal should be uniform through out.17. Finished borders should curve gently.18. Metal should not be highly polished on the tissue surface.19. All borders on soft tissue should be beaded fading out
near gingival margins.20. Should not interfere and irritate the tongue.21. Should not alter the natural contour of the lingual surface
of the mandibular alveolar ridge or palatal vault.22. Should not impinge on oral tissues during function.23. Should not retain or trap food particles.24. Aids in support, retention and stability.
Essays 19
Types of maxillary major connectors
1. Single posterior palatal bar.2. Single palatal strap.3. Anterior posterior palatal bar (Double palatal bar).4. U-shaped palatal connector (Horse-shoe).5. Combination anterior and posterior palatal strap-type
connector (Closed horse shoe shaped).6. Palatal plate-type connector (Complete palate).
Single palatal bar
Is a narrow half oval shaped bar with the maximum thicknessat the centre.
Gently curves along the palatal contour with the junctionssmoothly joining with the denture base.
Disadvantages
1. To maintain rigidity it should possess bulk causing tongueinterference.
2. Decreased vertical support to prosthesis.3. Cannot replace more than two teeth on each side of the
arch.4. Cannot be used in distal extension bases.
Advantages
Design for interim partial denture.
Figure 5: Single palatal bar
20 Review of Removable Partial Dentures
Single palatal strap
It is a wide, thin band of metal that crosses the palate. Theminimum thickness of Palatal strap is 8 mm.
Depending on the edentulous space the palatal strap can bemade wider.
Can be used for unilaterally edentulous situation.
Advantages
1. Greater resistance to displacing forces than a palatal bar.2. Better patient comfort.
Disadvantages
1. Less rigidity compared to complete coverage majorconnector.
2. Papillary hyperplasia can occur.
Figure 6: Single palatal strap
Anterior Posterior Palatal Bar (Double Palatal Bar)
It consists of a flat narrow anterior bar positioned in thevalleys of rugae.
It also consists of a half oval posterior bar. The anteriorand posterior bars are joined by flat longitudinal elementsin the lateral slopes of palate.
Advantages
1. It is rigid.2. Can replace anterior and posterior abutments.
Essays 21
3. Less palatal coverage which is comfortable to the patient.4. It is an ideal design for patients with large palatal tori.
Disadvantages
1. Less support.2. Can be used only when there is good periodontal support.3. Cannot be used in high palatal vaults.4. Tongue interferences are present.
Figure 7: Double palatal bar (Anteriorposterior palatal bar
U-shaped Palatal Connector (Horseshoe)
It is a thin band of metal along the lingual surfaces of toothextending to the palatal slopes. Thickness of the plate shouldbe minimum 6 to 8 mm.
The borders can either extend from gingival margin to palatalslopes or from lingual aspect of the tooth to palatal slopes.The palatal borders should end at the junction of horizontaland vertical slopes of the palate.
Advantages
1. Ideal for replacement of missing anterior tooth.2. This design provides some vertical support and indirect
retention.3. Can be designed in case of palatal tori.
Disadvantages
1. Cannot be given in distal extension partial denture as itflexes on loading.
2. Difficulty in speech and patient discomfort can occur.
22 Review of Removable Partial Dentures
Figure 8: U-shaped palatal connector
Anterior and posterior palatal strap-type connector (Closedhorse shoe shaped)
It consists of an anterior strap, which can be placed on thelingual aspect of tooth, or it should be placed 6 mm awayfrom gingival margin, if anterior tooth are not replaced.
It also consists of a posterior strap, which should be placedposteriorly but without contacting the soft palate.
Advantages
1. It is rigid and can replace anterior and posterior tooth.2. Can be given in cases of palatal tori.
Disadvantage
Speech problems and tongue interference can occur.
Figure 9: Anterior-posterior palatal-strap
Essays 23
Palatal Plate-type Connector (Complete coverage)
The anterior border should either extend to the cingula ofthe tooth surface or be kept 6 mm short of gingival margin.
The posterior border should extend to the junction of softand hard palate.
Types
a. All acrylic resin.b. Combination of metal and acrylic (The anterior rugae area
in metal and posteriorly acrylic).c . All cast metal.
Advantages
1. Good rigidity and support.2. Better retention.3. Maximum tissue coverage.4. Can be given for bilateral distal extension.5. Better stability in flat or flabby ridges.6. Can be designed in obturator patients.7. Design for transitional dentures (All acrylic).8. Natural sensation during eating and drinking as in All
metal.9. Can be relined later.
Disadvantages
1. Large area of tissue coverage can cause tissue reactions ashyperplasia.
2. Speech difficulties can occur.
24 Review of Removable Partial Dentures
DESCRIBE MANDIBULAR MAJOR CONNECTORS. ADD A NOTEON THE ADVANTAGES AND DISADVANTAGES OF EACHMANDIBULAR MAJOR CONNECTOR.
Definition
A major connector is the unit of the partial denture thatconnects the parts of the prosthesis located on one side of thearch with those on the opposite side. It is that unit of thepartial denture to which all other parts are directly or indirectlyattached.
Types of Mandibular Major Connectors
1. Lingual bar.2. Lingual bar with continuous bar retainer (Kennedy Bar).3. Linguoplate.4. Labial bar.
Lingual Bar
Shape and size: A 6-gauge half-pear-shaped bar (5 mm) inwidth located above moving tissues but as far below the gingivaltissues as possible.
Borders: Has two borders: Superior and inferior. The superior border should be tapered to the tissues above,
with its greatest bulk at the lower border. It is flat on thetissue side and having the greatest bulk in the inferior third.
Inferior border of the lingual bar is slightly rounded sothat it will not impinge on the lingual tissue when thedenture bases rotate inferiorly under occlusal loads. Themajor connector should not have sharp margins.
Location: The inferior border should be located so that it doesnot impinge on the tissues in the floor of the mouth duringswallowing, speaking, and other normal functions.
The location should not interfere with the resting tongueand cause trapping of food.
The superior border should be located 3 mm away fromgingival margins of teeth.
Essays 25
Minimum space required: At least 8 mm of vertical spacebetween the floor of mouth and gingival margin is required.
Measuring the height of floor: The first method is to measure the height of the floor with
a periodontal probe in relation to the lingual gingivalmargins of adjacent teeth with the tip of the patientstongue lightly touching the vermilion border of the upperlip. (More accurate).
The second method is to use an individualized impressiontray with its lingual borders 3 mm short of the elevatedfloor of the mouth and then use an impression material thatwill be accurately moulded as the patient licks the lips.
The inferior border of the lingual bar can be located at theheight of the lingual sulcus of the cast resulting from such animpression.
Advantages
1. Simplicity.2. Minimal tissue contact.3. Less plaque accumulation.
Disadvantages
1. Needs precise lab work.2. Cannot be placed when there is less than 8 mm of lingual
space.
Modifications
1. The thickness can be altered depending on the clinicalsituation to acquire more rigidity. This is accomplished byunderlying the ready-made form with a sheet of 24-gaugecasting wax.
2. Sublingual bar:The bar shape is same as that of a lingual bar.
Location: Lying over and parallel to the anterior floor of themouth.
26 Review of Removable Partial Dentures
Sublingual bar can be used along with a lingual plate ifthe lingual frenum does not interfere.
Can be used when an anterior lingual undercut exist wherelingual bar cannot be used.
Contraindications
1. When lingual tori exists.2. In cases of high lingual frenal attachment.3. High elevation of the floor of the mouth during functional
movements.
Figure 10: Lingual bar
Continuous bar retainer (Kennedys bar) or Double lingual bar
A continuous bar retainer is located on or slightly above thecingula of the anterior teeth along with a lingual bar. Theupper bar is also pear shaped and is 2 to 3 mm high with 1mm thickness. The bar should dip into the contact points ofteeth downward till upper limits of cingula.
The two bars are joined by minor connector located ininterproximal spaces usually between canine and premolar.
Indications
1. When a linguoplate cannot be given or if requires excessiveblockout of interproximal undercuts then a continuousbar can be used.
2. In cases of wide diastemae between the lower anteriorteeth.
Essays 27
Advantages
1. Enhance indirect retention.2. Provides horizontal stabilization to the prosthesis.3. Marginal gingiva receives natural stimulation.4. Can be used in large interproximal embrasures.
Disadvantages
1. Tongue annoyance.2. Entrapment of food.3. Proper fit is difficult to achieve with upper bar of double bar.
Modifications (Step back design): The upper bar can be stepbacked in between each tooth as in cases of diastema, henceaesthetically pleasing.
Figure 11: Double lingual bar (NL) or below diagram
Linguoplate
Shape
It is a pear shaped lingual bar with a thin solid piece of metalextending upward from superior border of bar to the lingualsurfaces of teeth.
A Linguoplate should be contoured to follow the contours ofthe teeth and the embrasures.
The upper border should follow the natural curvature of thesupracingular surfaces of the teeth also coveringinterproximal spaces to the contact points (Scallopedappearance).
28 Review of Removable Partial Dentures
All gingival crevices and deep embrasures must be blockedout parallel to the path of placement to avoid gingivalirritation and wedging effect between the teeth.
The Linguoplate should have a terminal rest at each end(commonly cingulum rest on canines or mesial fossae reston first premolars).
Material of choice-Chrome cobalt alloy.
Modification: Cut back or step back design to hide metalbetween wide spaced teeth without compromising the rigidityof the connector. Here the upper bar drops gingivally alongthe marginal ridge of tooth to cross gingiva to the other toothand rises up the marginal ridge to the contact point.
Indications
1. When the lingual frenum is high or the space available fora lingual bar is limited.
2. In Class I situations in which the residual ridges haveundergone excessive vertical resorption. Here Linguoplatewill use remaining teeth to resist horizontal rotations.
3. For stabilizing periodontally weakened teeth. (A continuousbar retainer).
4. When the future replacement of one or more incisor teethwill be facilitated by the addition of retention loops to anexisting Linguoplate.
5. In wide diastemae.
Advantages
1. Can be used in Class 1 situation when indirect retention isrequired.
2. In periodontally weak tooth lingual plate acts as splint.3. Can be used with some modification to prevent supra
eruption of mandibular anterior teeth.4. Of all the mandibular major connectors lingual plate has
maximum retention, support and stability.
Essays 29
Disadvantages
1. Irritation of soft tissues.2. Caries prone.
Figure 12: Linguoplate
Labial Bar
Shape
It is half pear shaped similar to lingual bar extending onto the labial surface and some time to the facial surface ofthe posterior tooth.
Relief is required below the bar.
Indications
1. Extreme lingual inclination of the remaining lowerpremolar and incisor teeth. This should be rectified bymouth preparation and restoration before planning for alabial bar.
2. Large mandibular tori.
Modification: Swing-Lock design, which consists of a labialor buccal bar that is connected to the major connector by ahinge on one end and a latch at the other end.
Support is by multiple rests on the remaining natural teeth.Stabilization and reciprocation by linguoplate contacting theremaining teeth and by the labial bar with its retentive struts.
Retention is by bar-type retentive clasp arms projectingfrom the labial or buccal bar.
Use of the Swing-Lock
1. Unfavourable tooth contours.
30 Review of Removable Partial Dentures
2. Unfavourable soft tissue contours.3. Teeth with questionable prognoses.
Contraindications1. Poor oral hygiene.2. Presence of a shallow buccal or labial vestibule.3. High frenal attachment.
Disadvantages1. Bulk of connector distorts lower lip.2. Patient discomfort.
Figure 13: Labial bar
Design of mandibular major connector
1. Outline of the basal seat areas on the diagnostic cast.2. Outline of the inferior border of the major connector.3. Outline of the superior border of the major connector.4. Unification by minor connector.
EXPLAIN IN DETAIL VARIOUS TYPES OF MINOR CONNECTORS.ADD A NOTE ON THE FUNCTIONS OF MINOR CONNECTOR.
Minor Connectors
Definition: Minor Connector is that component that joins otherunits of the prosthesis such as clasps, rests, indirect retainersand denture bases to the major connector.
Types of minor connector1. Joins the clasp assembly to the major connector.2. Joins indirect retainers or auxiliary rests to major
connector.3. Joins the denture base to the major connector.
Essays 31
4. Serves as an approach arm for a vertical projection orbar-type clasp.
I. Minor connectors that join clasp assembly to the majorconnector
They should be rigid, as they support the retentive claspand occlusal rest.
To have rigidity they need to have sufficient bulk.
Location: Minor connectors that support clasp assembliesare located on proximal surfaces of teeth adjacent to edentulousareas or in the embrasure between two teeth.
Shape: Broad buccolingually and thin mesiodistally. Thethickest portion buccolingually, should be at the lingual lineangle of the tooth and taper evenly to its thinnest point at thebuccal line angle of the tooth.
Figure 14: Minor connector joining clasp assembly
II. Minor connectors that join indirect retainers or auxiliaryrests to major connector
They arise from auxiliary rests. They should join the majorconnector at right angle.
The joining junction should be a gentle curve.
Location: In the embrasure between teeth to prevent tongueannoyance.
Figure 15: Minor connectorjoining indirect retainer
32 Review of Removable Partial Dentures
III. Minor connectors that join denture base to major connector
Types of denture base
1. Latticework construction2. Mesh construction3. Bead, wire, or nail-head minor connectors.
1. Open latticework construction:
Consists of two longitudinal struts with smaller strutsconnecting the two longitudinal struts.
Maxillary design: This consists of two metal struts, 12 and 16gauge thick.
The first extends longitudinally along the edentulous buccalridge in maxillary arch.
The border of the major connector acts as the second strut.
Mandibular design: In the mandibular arch one strut shouldbe positioned buccal to the crest of the ridge and the otherlingual to the crest of the ridge.
Smaller struts: 16 gauge thick smaller struts, connect the twostruts and form the latticework.
They run over the crest of the ridge and are positioned sothat there is no interference to arrangement of the artificialteeth.
Number of small struts: Commonly one cross strut betweeneach teeth to be replaced.
Figure 16: Minor connector joining denture base
Advantages
1. Strongest attachment of the acrylic resin denture base tothe removable partial denture.
Essays 33
2. Easy to reline.3. For multiple teeth replacement.
Mesh Construction
It is a thin sheet of metal with multiple small holes that extendsover the crest of the residual ridge to the same buccal, lingualand posterior limits, as does the latticework minor connector.
Indication: When multiple teeth are to be replaced.
Disadvantages
1. Difficult for the acrylic resin to flow through the small holes.2. Mesh type is a weak attachment.
Relief
After the wax forms of the struts are positioned on therefractory cast, a relief space is provided over theedentulous ridges for both the latticework and the meshminor connectors.
This relief is provided to create a space between the strutsand the underlying ridge around which the acrylic resindenture base will be retained.
Tissue stop: In distal extension partial dentures usinglatticework or mesh retention, the framework needs to bestabilized during the acrylic resin packing and processing.
As the acrylic resin requires some pressure to be forcedthrough the latticework and mesh minor connectors, theframework can displace or distort, hence a tissue stop is requiredto support the terminal portion of the minor connector.
Method
1. Tissue stop is made by removing 2 square mm of the reliefwax beneath the latticework.
2. The wax is removed from the point where the posterior endof the minor connector crosses the centre of the ridge.
34 Review of Removable Partial Dentures
3. During waxing of the framework, this depression is waxedas a projection of the latticework or mesh.
4. After the framework has been cast this projection willcontact the edentulous ridge of the cast and will preventthe framework from being distorted during acrylic resinpacking procedures.
Bead, wire, or nailhead retention:
The bead, wire, or nailhead minor connector is used withmetal denture bases.
No relief is provided beneath the minor connector as theacrylic resin mechanically bonds with the nail head or beadof the minor connector.
Mechanical retention:
Can be made by placing beads of acrylic resin polymer onthe waxed denture base and investing, and casting thesebeads.
Wires or form of nailheads that project from the metal basecan be used.
Disadvantages
1. It is difficult to adjust the metal base.2. Cannot be relined in case of ridge resorption.3. Weakest of the three types of attachment.4. Can be only on tooth-supported, well-healed ridges.5. Cannot use when interarch space is limited.6. No strength to withstand the forces of occlusion.
Advantages
1. Hygienic because of better soft tissue response to metal.2. Function successfully as better fit than acrylic denture base.
Attachment of minor connector to major connector
Should be joined to major connector with adequate bulkto withstand occlusal forces and to prevent from breakage.
Essays 35
The acrylic resin processed around the latticework andmesh minor connector should join the major connector ina smooth, even joint.
To prevent acrylic resin from being thinned in order toproduce a smooth joint, a space for a butt joint is placedin the design.
The butt joint aids the acrylic resin to blend evenly withthe major connector.
Finish lines/Butt joints
As acrylic resin is processed around the latticework and minorconnectors, space for these butt joints are made on bothinternal and external surfaces of the major connector.
In the case of nail head minor connector, the acrylic resinis processed only on the external surface, so only a single finishline is required.
Types
External Finish lines Internal Finish lines.
External finish lines
If they occur on the outer aspect of the major connector. External finish line must be sharp and definite with a slight
undercut to retain acrylic resin to the major connector. The angle, the finish lines form with the major connector
should be less than 90 degrees.
Method of placement: Formed by placement of the wax duringthe waxing procedure and by carving the wax.
Location
1. Should extend onto the proximal surfaces of the teethadjacent to the edentulous space.
2. Should begin at the lingual extent of the rest seat andcontinue down the lingual aspect of the minor connectoron the proximal surface of the tooth.
36 Review of Removable Partial Dentures
Internal finish lines
Are on the tissue side of the major connector.
Method of placement
Formed from the relief wax used over the edentulous ridgeson the master cast before duplication on which the frameworkwill be waxed.
A 24 to 26 gauge relief wax, placed under latticework ormesh minor connectors creates space for acrylic.
The same relief waxes margins become the internal finishline.
The ledge created by the margin of the wax must be sharpand definite.
Minor connectors that serve as approach arm for verticalprojection or bar-type clasp
Not required to be rigid unlike other minor connectors. It supports a gingivally approaching direct retainer. It should have a smooth, even taper from its origin to its tip. It must not cross a soft tissue undercut.
Figure 17: Approach arm
Functions of minor connector
1. Primary function is to join all the other components asclasps, rests, indirect retainers and denture bases to themajor connector.
2. Aids in efficient functioning of all components.3. Helps to retain rests in their rest seats, this serves to
transfer forces occurring against the prosthesis down thelong axis of the abutment teeth.
Essays 37
4. Minor connector aids in uniform distributing of the stresseshence, it should be rigid.
5. The minor connector distributes forces, on the edentulousridge to the ridge and the remaining teeth by transferringit to several other minor connectors that serve asattachments for clasps, rests, or indirect retainers.
6. Preservation of bone.7. In distal extension base the minor connector is part of the
saddle hence, holds the artificial tooth in proper alignment.8. Aids in retention, stability and support in a denture.
DEFINE A DIRECT RETAINER. LIST THE FUNCTIONS OF ACIRCUMFERENTIAL CLASP AND VARIOUS PARTS AS RELATEDTO FUNCTION. DESCRIBE THE VARIOUS TYPES OF RETAINERS.
Definition
A direct retainer is that component that engages an abutmenttooth and in doing so resists dislodging forces applied to aremovable partial denture.
Classification
1. Intracoronal retainers.2. Extra coronal retainers.
a. Circumferential or Akers claspb. Vertical projection or Roach clasp
Parts of circumferential claspa. Rest.b. Body.c. Shoulder.d. Reciprocal arm.e. Retentive clasp arm.f. Retentive terminal.g. Minor connector.
Functions of clasps1. Retention,2. Stability,3. Support,
38 Review of Removable Partial Dentures
4. Reciprocation,5. Encirclement,6. Passivity.
Parts of extra coronal direct retainers and specific function1. Rest: Function is vertical support2. Minor connector: Function is stabilization by acting through
guide planes placed on the proximal surfaces of abutmenttooth extending from the prepared marginal ridge to themiddle and gingival third of abutment tooth.
3. Clasp arms: Functions as stabilizing, retentive andreciprocating units.
Stabilization is attained by rigid portion of retentivearm and reciprocal arm along with the minorconnector.
Reciprocation is attained by reciprocal arm Retention is attained by retentive arm especially the
retentive terminal.
The reciprocal clasp arm has three functions:1. Reciprocation against the action of the retentive arm. During
placement and removal, reciprocation is most needed as theretentive arm flexes over the height of contour.True reciprocation during placement and removal ispossible only if guide planes are placed.
2. The reciprocal clasp arm should resist against horizontalforces so rigid clasp arms, rigid minor connectors and a rigidmajor connector should be used.
3. If reciprocal clasp arm rests on a suprabulge surface of anabutment tooth lying anterior to the fulcrum line it acts asan indirect retainer.
Figure 18: Parts of circumferential clasp: A. Minor connector, B. Retentive arm,C. Occlusal rest, D. Reciprocal arm
Essays 39
Types of clasps
1. Circumferential clasp which approaches the retentiveundercut from an occlusal direction. (Occlusallyapproaching).
2. The bar clasp arm, which approaches the retentive undercutfrom a cervical direction. (Gingivally approaching).
Different types of circumferential clasps:1. Cast circumferential clasp.2. Simple circlet clasp.3. Reverse circlet clasp.4. Multiple circlet clasp.5. Embrasure or modified crib clasp.6. Ring clasp.7. Fish hook or Hairpin clasp8. Onlay clasp.9. Combination clasp.
Different types of bar clasps:1. T Clasp.2. Modified T Clasp3. Y Clasp4. I Clasp and I Bar.
Circumferential clasps
Cast circumferential clasp
It is the method of choice for tooth supported partial dentures.The retentive arm should originate above occlusal half withthe retentive terminal placed below height of contour andpointing occlusally.
Advantages
1. Good support, retention and reciprocation.2. Easy to repair.3. Less food retention compared to bar clasp.
40 Review of Removable Partial Dentures
Disadvantages
1. Large amount of tooth surface covered that can causedecalcification and caries.
2. Minimum flexibility and cannot be used in distal extensionbases.
3. Interferes with normal food flow pattern.4. Not aesthetic.
Simple circlet clasp
Choice for tooth supported partial denture. The clasp approachesundercut from edentulous area and engages undercut oppositeto edentulous space.
Advantages
1. Good support, stability, encirclement and very goodpassivity.
2. The most widely used clasp.
Disadvantages
1. Large amount of tooth surface covered that can causedecalcification and caries.
2. Minimum flexibility and cannot be used in distal extensionbases.
3. Interferes with normal food flow pattern.
Reverse circlet clasp
Used when undercuts are present near the edentulous space.Ideally bar clasp is the choice but in situations as soft tissueundercuts where bar clasp cannot be used reverse clasp isused.
Advantage
Good for distal extension partial dentures.
Essays 41
Disadvantages
1. Difficult to obtain occlusal clearance where there is tightocclusion between upper and lower teeth.
2. Can cause food entrapment if occlusal rest is not wellprepared.
3. Wedging effect as it is placed between two teeth.4. Not aesthetic.
Multiple circlet clasp
Consists of two opposing simple circlet clasps joined at theterminal end of reciprocal arms.
Used as a splinting effect of weak tooth.
Disadvantages
1. Large amount of tooth surface covered that can causedecalcification and caries.
2. Minimum flexibility and cannot be used in distal extensionbases.
3. Interferes with normal food flow pattern.4. Not aesthetic.
Figure 19: Multiple circlet clasp
Embrasure clasp
Consists of two simple circlet clasps joined at the body. Theclasp crosses the marginal ridge and facial surface of both theteeth and engage undercuts on the opposite sides of therespective teeth. Used on side where there is no edentulous
42 Review of Removable Partial Dentures
space. Embrasure clasps should have two retentive clasp armsand two reciprocal clasp arms, either bilaterally or diagonallyopposed.
Disadvantages
1. Occlusal rest should be prepared on both the teeth.2. Difficult to get occlusal clearance.3. Large amount of tooth surface covered that can cause
decalcification and caries.4. Minimum flexibility and cannot be used in distal extension
bases.5. Interferes with normal food flow pattern.6. Not aesthetic.
Indication
When spacing is present between two teeth.
Figure 20: Minor connector joiningclasp assembly
Ring clasp
Ring clasp, encircles nearly all of a tooth from its point of origin.It is used when a proximal undercut cannot be approached byother means as in a distobuccal or distolingual undercut.
The ring-type clasp should be used on protected abutmentsas it covers such a large area of tooth surface.
Disadvantages
1. Not esthetic.2. Large amount of tooth surface covered that can cause
decalcification and caries.3. Minimum flexibility and cannot be used in distal extension
bases.4. Interferes with normal food flow pattern.
Essays 43
Figure 21: Ring clasp
Fish hook or Hairpin clasp
It is a simple circlet clasp in which the retentive arm crosses thefacial surface of the tooth and loops back in a hairpin turn toengage the undercut below its point of origin. The upper armacts as a minor connector and is rigid; the lower arm is taperedand is flexible.
Disadvantages
1. Only can be used in tooth with adequate occlusogingivalheight.
2. There tends to be food accumulation between the upper andlower clasp arms.
3. The upper arm can cause occlusal interference in tightocclusion of upper and lower arch.
4. Caries prone.5. Not aesthetic.6. Large amount of tooth surface covered that can cause
decalcification and caries.7. Minimum flexibility and cannot be used in distal extension
bases.8. Interferes with normal food flow pattern.
Figure 22: Fish-hook clasp
44 Review of Removable Partial Dentures
Onlay clasp
It covers the entire occlusal surface with buccal and lingualclasp arms.
Should be made in patients with good oral hygiene. Occlusal surface should be of gold or acrylic.
Indication: To correct occlusal plane discrepancies as in toothtipping or rotation.
Figure 23: Onlay clasp
Combination clasp
Consists of a wrought wire retentive terminal and cast reciprocalarm. The wrought wire can be incorporated during wax up orcan be soldered later on.
Indications
1. In distal extension partial denture with mesiobuccalundercut.
2. Can be used in deeper undercuts due to its flexibility.
Disadvantages
1. Requires additional work during laboratory fabrication.2. Chances of breakage.3. Easily distorted during normal handling.4. Less bracing and stabilization compared to other
circumferential clasp.
Advantages
1. Flexibility.2. Adjustability.
Essays 45
3. Aesthetic advantage over other retentive circumferentialclasp arms.
4. Minimum of tooth surface is covered compared to a castclasp arm.
5. Fatigue failures are less compared to a cast, half-roundretentive arm.
Bar clasp or Roach clasp
The bar clasp arm has been classified by the shape of the retentiveterminal as T, modified T, I, Y, or almost any letter clasp arm.
They originate from the framework or base and approachthe undercut from a gingival direction.
Flexibility is adjusted depending on the taper and length ofthe approach arm.
Advantage : It is more esthetic.
Disadvantages: Causes food entrapment.Less bracing an stabilization compared to C- Clasp.
Rules of use
1. Approach arm should not impinge on soft tissues.2. Minor connector attached to bar clasp should be rigid.3. Approach arm should be uniformly tapered and should
cross the gingival margin at 90 degrees.4. Approach arm should extend to the height of contour.5. The bar clasp is used only if the retentive area is adjacent to
edentulous.6. Retentive terminal of bar clasp should point toward the
occlusal surface.7. Bar clasp should be placed as low on tooth as possible.
I Bar is a part of the RPI system (rest, proximal plate, I-bar). This clasp assembly consists of a mesio-occlusal rest with
the minor connector placed into the mesiolingualembrasure.
A distal guiding plane, extending from the marginal ridgeto the junction of the middle and gingival thirds of the
46 Review of Removable Partial Dentures
abutment, is prepared to receive a proximal plate. Theproximal plate, in conjunction with the minor connectorsupporting the rest, provides the stabilizing and reciprocalaspects of the clasp assembly.
The l-bar should be located in the gingival third of thebuccal or labial surface of the abutment in 0.01 inch-undercut.
ENUMERATE VARIOUS FACTORS AFFECTING RETENTION INDIRECT RETAINERS. ADD A NOTE ON GINGIVALLYAPPROACHING CLASPS AND RPI SYSTEM.
Factors affecting retention
1. Flexibility of the clasp arm,2. The depth that the retentive terminal extends into the
undercut,3. The amount of clasp arm that extends below the height of
contour,4. The amount of retention used should always be the minimum
necessary to resist reasonable dislodging forces.The retentive undercut has three dimensions: The buccolingual depth of the undercut expressed in
thousandths of an inch. The less sharp this angle, thegreater distance needed between the height of contourand the retentive terminal to achieve the same amountof retention.
The distance between the survey line and the tip of theretentive clasp. This affects the clasp arm length, andin turn influences the flexibility of the clasp.
Mesio-distal length of the clasp arm below the heightof contour. The longer this measurement, the moreflexible the clasp will be and the more important is thebuccolingual dimension of the retentive undercut.The most variable factor in determining retention fora removable partial denture is clasp flexibility.
Essays 47
Flexibility is determined by
1. The length of the clasp,2. The diameter of the clasp arm,3. Its taper, the cross-sectional form and4. The material from which the clasp is made.
Length
The greater the length of the clasp arm, the greater will be itsflexibility. By doubling the length of a clasp arm, its flexibility isincreased five times. Flexibility should be just adequate enoughto provide retention.
Diameter
Flexibility is inversely proportional to the diameter of the clasparm. A uniform taper in both thickness and width is essentialfor both the approach arm of a bar clasp and the retentive armof a cast clasp. A clasp should be half as thick at the tip as at theorigin.
Cross-sectional form
A round clasp has the ability to flex in all spatial planes, whereasa half-round clasp flexes only in a single plane.
Material
Chrome alloys have a higher modulas of elasticity than dogold alloys and are therefore less flexible.
Example: Chrome alloy clasps are placed in undercut of 0.01inch. Gold alloys are placed in 0.015 inch.
As internal structure of wrought wire has greater ability toflex than the crystalline structure of cast alloy; a greater depthof undercut is required for a wrought wire clasp than for acast clasp. Eg: 0.020 inch.
Details of bar or vertical projection clasps
Vertical projection clasps approach retentive undercut froma gingival direction. Hence, called as push type of retention.
48 Review of Removable Partial Dentures
The flexibility of the bar clasp can be controlled by thetaper and length of the approach arm. The greater thelength and taper, the more the flexibility of the clasp.
As the bar clasp is gingivally approaching, it is moreesthetic than a circumferential clasp.
Disadvantages
1. Tendency to collect food debris.2. Increased flexibility of the retentive arm, decreases bracing
and stabilization. Additional stabilizing units need to be addedto attain bracing and stabilization.
Rules for use
1. The approach arm of the bar clasp must not impinge on thesoft tissue it crosses.
2. The minor connector that attaches the occlusal rest to theframework should be strong and rigid.
3. The approach arm must always be tapered uniformly.4. The approach arm must never be designed to bridge a soft
tissue undercut.5. The approach arm should cross the gingival margin at a 90-
degree angle.6. The bar retentive clasp is used only when the retentive
undercut is adjacent to the edentulous area from which theapproach arm originates.
7. The reciprocal arm is positioned above the height ofcontour. The retentive terminal tip must point toward theocclusal surface.
8. The bar clasp should also be placed as low on the tooth aspossible.
Types of Bar ClaspsT Clasp
Used often along with cast circumferential reciprocal arm. The retentive terminal and its opposing terminal project
laterally from the approach arm to form a T.
Essays 49
Both terminals should point toward the occlusal surfaceof the abutment tooth.
The retentive terminal must cross the height of contour toengage the retentive undercut, while the other terminal isplaced on the suprabulge of the tooth.
The approach arm contacts the tooth only at the height ofcontour.
Uses
1. In distal extension ridge with distobuccal undercut.2. It reduces the torque to abutment tooth.3. Can also be used for tooth-supported partial denture if
the retentive undercut is located adjacent to the edentulousspace.
Disadvantages
1. The T clasp can never be used when soft tissue undercut ispresent.
2. If used causes food retention and irritation to the lips andcheeks.
3. Never to be used when the height of contour is close tothe occlusal surface of an abutment tooth.
4. Not to be used in mesiobuccal undercuts.
Modified T Clasp
The modified T clasp is a clasp in which only one terminal ispresent (only the retentive terminal). The nonretentive (usuallymesial) finger is omitted.
Uses: Used on canines or premolars for esthetic.
Disadvantage
1. 180-degree coverage is not present which can compromiseother functions of clasp such as bracing and reciprocation.
2. Can never be used when soft tissue undercut is present.
50 Review of Removable Partial Dentures
3. If used causes food retention and irritation to the lips andcheeks.
4. Never to be used when the height of contour is close tothe occlusal surface of an abutment tooth.
5. Not to be used in mesiobuccal undercuts.
Y Clasp
This is commonly used when the height of contour on thefacial surface of the abutment tooth is high on the mesial anddistal line angles but low on the centre of the facial surface.
The rest of the rules are same as T-clasp.If recontouring can help to bring the survey line to the
middle, a T-clasp can be used.
I Clasp and I Bar
Use: Used on the distobuccal surface of maxillary canines.
Disadvantage: Encirclement and horizontal stabilization arecompromised.
Figure 24: Types of clasp; A. I-bar, B. T clasp, C. Modified T clasp
RPI
The clasp system includes the three elements (Kratochvilssystem): mesial rest, proximal plate and I bar.
Krols criteria
1. Rest preparations are less extensive in the RPI system. Themesial rest prepared on molars and canines are often circularconcave depressions prepared in the mesial marginal ridge.
Essays 51
2. Proximal plate is diminished in all directions and I barretentive tips are placed mesial to the mesiodistal heightof contour.
3. Occlusal force on extension base disengages proximal plateinto gingival concavity and I-bar disengages into interproximalembrasure.
Tipped abutments and tissue impingement are treated witha further modification, the RPA clasp (rest, proximal plate andAkers clasp).
When the Akers clasp arm is used, careful attention is paidto relieving all undercuts except at the retentive tip.
The requirements of a partial denture clasp system (verticalsupport, horizontal stabilization, retention, reciprocation andpassivity) are all met by the I-bar system.
Figure 25: RPI system, A. Mesial rest, B. Proximal plate,C. I-bar, D. Krols modification
DEFINE REST AND REST SEAT. GIVE ITS LOCATION. DESCRIBEVARIOUS TYPES OF RESTS AND THEIR FUNCTION.
Definition
Rest is a rigid extension of a fixed or removable partial denture,which contacts a remaining tooth or teeth to dissipate verticalor horizontal forces.
Any unit of a partial denture that rests on a tooth surfaceto provide vertical support is called a rest.
The prepared surface of an abutment to receive the rest iscalled the rest seat.
52 Review of Removable Partial Dentures
Depending on the location it is classified as
1. Occlusal rest.2. Cingulum rest/ lingual rest.3. Incisal rest.
Depending on the function it is classified as1. Primary rest.2. Secondary or Auxiliary rest.
Functions of rest Primary function is to provide vertical support for the partial
denture. Additional functions are:
1. Maintains components in their planned positions.2. Maintains established occlusal relationships.3. Prevents impingement of soft tissues.4. Directs and distributes occlusal loads to abutment teeth.5. Prevents cervical movement of partial denture.
Occlusal rest and rest seat
Shape
Triangular shape with the apex toward the centre of the occlusalsurface.
Base of the triangular shape at the marginal ridge shouldbe at least 2.5 mm for both molars and premolars.
Floor of the occlusal rest seat should be concave or spoonshaped.
Thickness
At the marginal ridge thickness should be minimum 1.5 mm.Preparation should be within enamel.
Angulation
The angle formed by the occlusal rest and the vertical minorconnector from which it originates should be less than 90degrees.
Essays 53
Method of preparation
Occlusal rest seats in sound enamel can be prepared with diamondpoints of the size of Nos. 6 and 8 round burs or with carbideburs.
The larger diamond is used to prepare the marginal ridgeand to establish the outline form of the rest seat. The smallerdiamond point deepens the floor of the occlusal rest seat makingit spoon shaped.
The unsupported enamel rods are planed by round bur ofsuitable size revolving at moderate speed.
Finally an abrasive rubber point is used to polish thepreparation.
Function
As a shallow ball-and-socket joint, hence able to resisthorizontal stresses to the abutment tooth.
Types
1. Interproximal occlusal rest seats.2. Internal occlusal rests.
Figure 26: Rests, A. Occlusal rest, B. Incisal rest, C. Cingulum rest
Interproximal occlusal rest seats
Rest seats that are prepared as adjoining occlusal rest seatswith preparations extending farther lingually.
54 Review of Removable Partial Dentures
Advantages
1. Avoids interproximal wedging by the framework.2. Prevents food entrapments.
Rules for preparation
1. Contact points of abutment teeth should be preserved.2. Sufficient tooth structure removed to allow for adequate bulk.3. Shaped so that occlusion will not be altered.4. Sufficient space must be created to avoid interference with
placement of rests.
Internal occlusal rests
Used in totally tooth-supported situations.Enhances occlusal support and horizontal stabilization.Occlusal support is derived from the floor of the rest seat and
horizontal stabilization from the near-vertical walls.
Preparation: Rest should be parallel to the path of placement.Tapered occlusally and slightly dovetailed to prevent
dislodgement proximally.
Advantages
1. Aesthetically pleasing.2. Can locate rest seat in a favourable position in relation to
the horizontal axis of the abutment.3. Retention is provided by a lingual clasp arm.4. Use of a machined mandrel made of a chromium-cobalt alloy
can be waxed into the crown or inlay pattern, invested andcasted to a position parallel to the path of placement.
Rules for rest seat preparations
1. Should be prepared in enamel.2. For effective functioning of rest guide plane preparations
should be done.3. The preparation of occlusal rest seats must follow proximal
preparation, never precede it.
Essays 55
4. A fluoride gel should be applied to abutment teethfollowing enamel recontouring after the impressions aremade.
5. Occlusal rest seat preparations in existing restorations aretreated the same as preparations on tooth.
6. When a primary rest seat preparation is not adequate infunction, a secondary occlusal rest should be used on theopposite side of the tooth to prevent slipping of the primaryrest.
7. Occlusal rest seats in new restorations should be placed inthe wax pattern.
8. Occlusal rest seats in crown and inlays are generally madesomewhat larger and deeper than those in enamel.
9. Occlusal rest seats supporting tooth-borne dentures aremade slightly deeper than those supporting distal extensionbases.
Cingulum rests on canines
Sufficient space must be present or created to avoidinterference with placement of rests.
A lingual rest is preferable to an incisal rest because it isplaced nearer the horizontal axis of rotation (tipping) of theabutment.
Lingual rests are more aesthetically acceptable than areincisal rests.
Should be placed in enamel.
Shape of rest seat
A slightly rounded V.
Location
On the lingual surface at the junction of the gingival and middleone third of the tooth.
Apex of the V is directed incisally.
56 Review of Removable Partial Dentures
Method of preparation
1. Preparation is started with an inverted cone-shapeddiamond stone and progressing to smaller, tapered stoneswith round ends to complete the preparation.
2. All line angles should be eliminated.3. Shaped, abrasive rubber polishing points, with pumice, is
used for polishing.
Rules for preparation
Prepared after finalizing the path of placement. The floor of the rest seat should be toward the cingulum. No enamel undercut, should be present. Ideally, it is best to place the rest seat in a cast restoration. The lingual rest can also be placed on the lingual surface of
a cast veneer crown, a three-quarter crown, or inlay. Cast chromium-cobalt alloy rest seat attached to lingual
surfaces of anterior teeth by composite resin cements havebeing tried.
Incisal rests and rest seats Incisal rests are placed at the incisal angles of anterior
teeth and on prepared rest seats. Incisal rests are placed on enamel. Incisal rests are used as auxiliary rests or as indirect
retainers. Can be placed in mandibular canines also.
Shape
Incisal rest seat is a rounded notch at an incisal angle or on anincisal edge, with the deepest portion of the preparation apicalto the incisal edge. The rounded notch is bevelled labially andlingually and the lingual enamel is shaped to accommodateminor connector connecting the rest to the framework.
Size
Incisal rest seat is 2.5 mm wide and 1.5 mm deep.
Essays 57
Function
1. As auxiliary rest.2. As indirect retainer to prevent rotational movement of the
denture base.
Primary rest
It is a rest seat prepared to support the clasp assembly and actas a vertical support in preventing the displacement of thedenture in cervical direction.
Secondary or auxiliary rest
Function as indirect retainer in distal extension partial dentures.The indirect retainers are placed opposite to fulcrum lineanteriorly.
Figure 27: Rests 1. Primary rest, 2. Secondary rest
Factors influencing effectiveness of indirect retainers
1. Depends on effective function of the direct retainers.2. To assess the position of placement of indirect retainer three
areas must be considered:a. Length of the distal extension base,b. Location of the fulcrum line,c. At what distance the indirect retainer should be placed.
3. Rigidity of the connectors supporting the indirect retainer.4. Abutment tooth health and position.
58 Review of Removable Partial Dentures
Auxiliary functions of indirect retainers
1. Reduces the anteroposterior movement on the principalabutments.
2. Aids in horizontal stabilization when made parallel to thepath of placement.
3. Splinting effect when used in the anterior teeth assupporting indirect retainers.
4. Aids in supporting major connector from settling into thetissues.
5. First visual indications for the need to reline in distalextension base partial denture.
Forms of indirect retainers
1. Auxiliary occlusal rest
In Class I-Bilateral rests on the mesial marginal ridge of thefirst premolars.
In Class II partial dentures- Placed on the margin
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